In recent years, in the production of semiconductor elements and liquid crystal display elements, advances in lithography techniques have lead to rapid progress in the field of patterns miniaturization. Typically, these miniaturization techniques involve shortening the wavelength of the exposure light source. Conventionally, ultraviolet radiation typified by g-line and i-line radiation has been used, but nowadays mass production of semiconductor elements using KrF excimer lasers and ArF excimer lasers has commenced. Furthermore, investigation is also being conducted into the use of radiation with even shorter wavelengths than these excimer lasers, such as F2 excimer lasers, electron beams, EUV (extreme ultraviolet radiation), and X-rays.
Furthermore, one example of a known pattern-forming material capable of forming a pattern of minute dimensions is a chemically amplified resist, which includes a base material component with a film-forming capability, and an acid generator component that generates an acid upon exposure. Chemically amplified resists include negative type, which undergo a reduction in alkali solubility on exposure, and positive type, which display increased alkali solubility on exposure. These resist materials are typically dissolved in an organic solvent prior to use.
Polymers with a weight average molecular weight of approximately 5,000 or greater have conventionally been used as the base material component for these types of chemically amplified resists, and examples of these polymers include polyhydroxystyrene (PHS), PHS-based resins in which a portion of the hydroxyl groups have been protected with acid-dissociable, dissolution-inhibiting groups, and copolymers derived from acrylate esters and/or methacrylate esters, all of which exhibit a high degree of transparency relative to a KrF excimer laser (248 nm) or the like. Furthermore, onium salt-based acid generators are the most widely used acid generators. As the organic solvent, solvents such as propylene glycol monomethyl ether acetate (hereafter abbreviated as PGMEA) and ethyl lactate (hereafter abbreviated as EL) are typically used, either alone, or as part of a mixed solvent.
However, when a pattern is formed using these types of materials, a problem arises in that roughness can develop on the upper surfaces and side wall surfaces of the pattern.
This type of roughness has conventionally posed few problems. However in recent years, with the rapid miniaturization of semiconductor elements and the like, ever higher levels of resolution such as width dimensions of no more than 90 nm are being demanded, and this miniaturization has meant that roughness is becoming a more serious problem. For example, when a line pattern is formed, roughness on the side wall surfaces of the pattern known as LER (line edge roughness) causes fluctuation in the line width that is formed. The controlled degree of this fluctuation in the line width is required to be suppressed to no more than approximately 10% of the width dimension, and the effects of LER increase as the pattern dimensions are reduced. For example, when a line pattern with dimensions of approximately 90 nm is formed, the controlled degree of the fluctuation in the line width is preferably suppressed to no more than approximately 10 nm.
However, the polymers typically used as base materials have a large root mean square radius per molecule of several nm, and therefore the degree of fluctuation described above is equivalent to the width of only a few polymer molecules. As a result, as long as such polymers are used as the base material component, reductions in LER will remain extremely difficult to achieve.
On the other hand, the use of low molecular weight materials containing alkali-soluble groups such as hydroxyl groups, wherein either a portion of, or all of, those groups are protected with acid-dissociable, dissolution-inhibiting groups, as the base material has also been proposed (for example, see patent documents 1 and 2). These low molecular weight materials have small root mean square radius values as a result of their lower molecular weight, and as such, their contribution to increase of LER is expected to be small.
However, even when these low molecular weight materials are used, achieving a satisfactory improvement in LER remains difficult, and further reductions in the level of LER are still keenly sought.
[Patent Document 1]
Japanese Unexamined Patent Application, First Publication No. 2002-099088
[Patent Document 2]
Japanese Unexamined Patent Application, First Publication No. 2002-099089